The present invention generally relates to inhibiting particle transport in an ion beam and, more particularly to a system and method for providing an electrostatic system for inhibiting transport of microscopic particles within an ion beam.
In the manufacture of semiconductor devices, an ion implanter is employed to dope a semiconductor wafer or glass substrate with impurities. In particular, ion beam implanters are used to treat silicon wafers with an ion beam, in order to produce n or p type extrinsic materials doping or to form passivation layers during fabrication of an integrated circuit. When used for doping semiconductors, an ion beam implanter injects a selected ion species to produce a desired extrinsic material. Implanting ions generated from source materials such as antimony, arsenic or phosphorus results in xe2x80x9cn typexe2x80x9d extrinsic material wafers, whereas if xe2x80x9cp typexe2x80x9d extrinsic material wafers are desired, ions generated with source materials such as boron, gallium or indium may be implanted.
Typical ion beam implanters include an ion source for generating positively charged ions from ionizable source materials. The generated ions are formed into a beam and directed along a predetermined beam path to an implantation station. The ion beam implanter may include beam forming and shaping structures extending between the ion source and the implantation station. The beam forming and shaping structures maintain the ion beam and bound an elongated interior cavity or passageway through which the beam passes en route to the implantation station. When operating an implanter, this passageway is evacuated to reduce the probability of ions being deflected from the predetermined beam path as a result of collisions with air molecules.
The mass of an ion relative to the charge thereon (e.g., charge-to-mass ratio) affects the degree to which it is accelerated both axially and transversely by an electrostatic or magnetic field. Therefore, the beam which reaches a desired area of a semiconductor wafer or other target can be made extremely pure since ions of undesirable molecular weight are deflected to positions away from the beam and implantation of other than desired materials can be avoided. The process of selectively separating ions of desired and undesired charge-to-mass ratios is known as mass analysis. Mass analyzers typically employ a mass analysis magnet creating a dipole magnetic field to deflect various ions in an ion beam via magnetic deflection in an arcuate passageway, which effectively separates ions of different charge-to-mass ratios.
The ion beam is focused and directed at a desired surface region of the substrate. Typically, the energetic ions of the ion beam are accelerated to a predetermined energy level to penetrate into the bulk of a workpiece. The ions are embedded into the crystalline lattice of the material to form a region of desired conductivity, with the beam energy determining the depth of implantation. Examples of ion implantation systems include those available from Axcelis Technologies of Beverly, Mass.
Operation of an ion implanter or other ion beam equipment (e.g., linear accelerators) may result in the production of contaminant particles. The contaminant particles, for example, may be less than about 1 xcexcm in size. The momentum of the ions in the beam that strike the particles, in turn, cause the particles to be transported with the beam, although typically at a speed much less than the ions. Consequently, particles entrained in an ion beam may be transported with the beam toward the wafer (or other substrate), resulting in undesired contamination at the wafer.
In an ion implantation system, for example, one source of contaminant particles is photoresist material. Photoresist material is coated on wafer surfaces prior to implantation and is utilized to define circuitry on the completed integrated circuit. As ions strike the wafer surface, particles of photoresist coating may be dislodged from the wafer and may become entrained in the ion beam. Contaminant particles that collide with and adhere to a semiconductor wafer or other substrate during ion implantation may be a source of yield loss in the fabrication of semiconductor and other devices that require submicroscopic pattern definition on the treated wafers.
As semiconductor devices are manufactured at reduced sizes with greater precision, higher accuracy and efficiency are required of apparatuses for manufacturing such semiconductor devices. Accordingly, it is desirable to reduce the level of contaminant particles in an ion beam so as to mitigate wafer contamination.
The present invention relates to a system and method for inhibiting the transport of a particle entrained in an ion beam. The particle within an ion beam is charged to a polarity during a first region of the system. A first electric field helps Another electrode downstream from the first electric field provides an electric field opposite the first electric field and provides a potential barrier, which repels the charged particle. As a result, the charged particle may be urged away from the direction of beam travel, suitably out of the ion beam. The potential barrier, for example, may urge a charged particle into an electrode where it, in turn, discharges to a neutral potential or to a location where it is unlikely to bounce back into the beam path. As a result, particles may be trapped or diverted from an ion beam in accordance with the present invention, thereby mitigating contamination of a workpiece.
Another aspect of the present invention provides a system for inhibiting transport of particles with an ion beam. The system includes a first electrode that provides a first electric field having a first polarity opposite that of the ion beam. A particle entrained in the ion beam within the first electric field is charged to a polarity matching the ion beam. A second electrode is located downstream in a direction of travel for the ion beam relative to the first electrode. The second electrode provides an electric field having a polarity matching the ion beam for repelling the charged particle away from the downstream direction of travel.
Yet another aspect of the present invention provides a system for inhibiting the transport of particles with an ion beam. The system includes a negative electrode that provides a negative electric field, which positively charges a particle entrained in the ion beam. A positive electrode is located downstream relative to the negative electrode. The positive electrode provides a positive electric field for repelling the positively charged particle away from the direction of travel.
Another aspect of the present invention provides an ion implantation system. The system includes an ion source for emitting ions to treat a substrate located at a downstream implantation station. An analyzing magnet system diverts ions of an appropriate mass to an implantation trajectory. A trap system inhibits transport of particles with the diverted ions from the analyzing magnet system. The trap system includes a first electrode that provides a first electric field having a first polarity opposite that of the ion beam. A particle entrained in the ion beam is charged to a polarity matching an ion beam formed of the diverted ions. A second electrode located in a downstream direction of travel for the ion beam relative to the first electrode provides an electric field having a polarity opposite the first electric field for repelling the charged particle. A substrate is supported at the implantation station for treatment with the ions provided by the trap system. As a result, particle contamination of the substrate is mitigated by the trap system.
Still another aspect of the present invention provides a method for inhibiting transport of particles with an ion beam. The method includes generating a first electric field in the path of the ion beam and charging particles located in the ion beam in a region of the first electric field with a polarity matching the ion beam. A second electric field is generated in the path of the ion beam downstream relative the first electric field. The second electric field has a polarity opposite the first electric field so as to repel at least some of the charged particles away from the ion beam.
Another aspect of the present invention provides a system for inhibiting transport of particles with an ion beam. The system includes at least one electrode energized to provide a negative electric field through which the ion beam travels. A particle entrained in the ion beam positively charges within the negative electric field and, in turn, is unable to pass through the system due to attractions provided by a negative potential well for the positively charged particles.